In general, a smart key system for a vehicle refers to a system for preventing a vehicle from being robbed by allowing various functional operation units of a vehicle body to be operated only when a driver (or a user) carries a fob key and a smart key unit (hereinafter, referred to as an SMK unit) authorizes that the driver (or the user) is an authorized user by decoding an encoding code applied from the fob key.
That is, when the user approaches the vehicle within a predetermined distance while carrying the fob key, the SMK unit wakes up the fob key, performs a procedure of authorizing an ID of the authorized user by mutually communicating encoding data of a transponder embedded in the fob key, and then switches operations of various functional operation units, such as starting an engine of the vehicle, opening/closing a trunk door, and opening/closing of a side door, to be operable when it is determined that the user is the authorized user.
However, when the side door is opened, a signal transfer system may be divided into two situations as described below. That is, the first case is a case where the SMK unit authorizes the authorized user ID, and then the user presses a switch related to an operation of the side door among the operation switches of the various functional operation units provided in the fob key and transmits a predetermined signal to the SMK unit, and the second case is a case where the SMK unit authorizes the authorized user ID, and then the user actively pulls a knob of the side door and transmits a triggering signal generated from the knob of the side door to the SMK unit.
In the meantime, the authorized user ID authorizing process performed between the SMK unit and the fob key in the smart key system in the related art will be briefly described below.
First, when the fob key approaches the vehicle within a predetermined distance or directly pulls the knob of the side door, a challenge signal is generated, and the generated challenge signal is modulated and demodulated by the SMK unit and is received by an LF receiver of the fob key.
When the fob key receives the challenge signal, a response signal including an encoding code is transmitted by using an RF transmitter of the fob key, the RF receiver of the SMK unit receives the response signal and determines whether the response signal is matched with a predetermined encoding code, and then enables the functional operation unit to be operated based on the fob key carried by the authorized user only when the response signal is matched with the predetermined encoding code.
However, even in a case where the user actually carrying the fob key goes beyond a predetermined distance (for example, a maximum visual distance, at which the driver views the vehicle) from the vehicle, the smart key system in the related art maintains a state in which a third party is capable of operating the various functional operation units when a normal challenge signal is transmitted to the fob key from the vehicle (which is referred to as a “relay attack”), so that there is a problem in that the vehicle or equipment stored in the vehicle may be robbed.
Particularly, in theory, when the fob key carried by the authorized user goes beyond a predetermined distance (a challenge signal reaching distance) from the vehicle, the fob key cannot receive the challenge signal, the aforementioned response signal including the encoding code itself is not transmitted, so that there may be no problem, but when a plurality of repeaters (a repeater 1 and a repeater 2) having an unlawful intention is provided between the vehicle and the fob key of the authorized user, there still occurs a problem in that a third party may break into the vehicle.